Apparatus for jacketing tubular stock

ABSTRACT

Upper and lower advancing means advance tubular stock in downward direction and in a predetermined path which comprises at least some superimposed helical convolutions of low pitch. A feed device is arranged at the upper end of the path and a takeup device is arranged at the lower end of the path for the tubular stock. Extruding means is arranged adjacent one of the convolutions for extruding onto the outer circumferential surface of the advancing tubular stock a circumferentially complete jacket of cellular synthetic plastic. Forming means is arranged adjacent a second convolution downstream of the extruding means forming the peripheral surface layer of the obtained jacket into a continuous smooth skin. Cooling means is arranged adjacent still a further convolution downstream of the forming means and cools the resulting jacketed tubular product.

0 United States Patent [151 snw nw Hartmann et a1. 51 Jan. W 19% 54]APPARATUS FOR JACKETING 2,952,037 9/1960 Ruck et al. ..1s/12 TF uxTUBULAR STOCK FOREIGN PATENTS OR APPLICATIONS [72] Inventors:Franz-Josef Hartmann, Paderdorn; Wilhelm Lachenmayer, Berlebeck Nr 392105,284 8/1942 Sweden ..18/13 5 both of Germany 192,566 8/1937Switzerland 1 ..18/12 TB [73] Assignee: Benteler-Werke AG, Paderborn,Germany Primary Examiner-J. Spencer Overholser AssistantExaminer-Michael 0. Sutton [22] Flled' 1969 AttorneyMichael S. Striker[21] Appl. No.: 884,919

[57] ABSTRACT [30] Foreign Application Priority Data Upper and loweradvancing means advance tubular stock in downward direction and in apredetermined path which com- 1968 Germany l8 14 8862 prises at leastsome superimposed helical convolutions of low pitch. A feed device isarranged at the upper end of the path [52] US. Cl ..425/71,425/113,442255/g5255, and a takeup device is arranged at the lower endof the path 51] Int Cl 1329f 3/10 for the tubular stock. Extruding meansis arranged adjacent I 58] Field 3 H 13 S one of the convolutions forextruding onto the outer circum- 12 121: TS 1 1 ferential surface of theadvancing tubular stock a circumferentially complete jacket of cellularsynthetic plastic. Forming means is arranged adjacent a secondconvolution [56] References Cited downstream of the extruding meansforming the peripheral UNITED STATES PATENTS surface layer of theobtained jacket into a continuous smooth skin. Cooling means is arrangedadjacent still a further con- 3,488,808 l/l970 Glbney ..18/l3 H volutiondownstream f the f i means and cools the i 31 ;211:358 a; resultingjacketed tubular product. 2,613I392 10/1952 Ternes ..18/14 A 14 Claims,8 Drawing Figures *l I l SHEET 1 OF 3 FIG.

INVENTO mu: Tour IMIUEJNW mam-A. n dAo/ew 7H ATTORNEY Pmmmmm 3535515 sum2 OF 3 FIG. 2

FIG. 3

INVENJQR 03 r "4 1w illi I56 600" 1(41/ ATTORN PATENTEDJAMIQH 3,635,615

SHEET 3 0F 3 UCUTTER FIG. 8

INVENTO an NW5 1 43 a (an 1/ ATTORNEY APPARATUS FOR JACKETING TUBULARSTOCK CROSS-REFERENCE TO COPENDING APPLICATIONS A copending applicationwas filed on Sept. 20, 1968 in the name of l-Ielmut Benteler et 21.; ithas Ser. No. 761,221 and is entitled Method of and Apparatus forjacketing Tubular Stock."

BACKGROUND OF THE INVENTION The present invention relates generally tothe jacketing of tubular stocks, and more particularly to the jacketingof bendable tubular stock with synthetic plastic material.

From the aforementioned copending application it is already known tocontinuously jacket a tubular stock with a thermally and acousticallyinsulating cover of cellular synthetic plastic. The cold or cool tubularmetallic stock is passed through the extrusion die of an extruder andjacketed with a mixture of preplastified foamable synthetic plasticmaterial and between 0.2 and L parts by weight of foaming agent. Thegases which develop and/or air are simultaneously withdrawn from theregion of initial contact between the synthetic plastic and the metallicstock. Subsequently the outer peripheral surface of the thus-producedjacket of foamed synthetic plastic is smooth and the thus-obtainedjacketed tubular product is cooled.

According to this previous application the mixture of plastic,preferably but not necessarily polyolefin, and foaming agent which ispreferably but not necessarily azodicarbonamide, is preplastified byheating to between approximately 180 and 225 C. and being subjected tofeed-screw pressure on the order of approximately 130 atmospheres. It isthereupon applied to the tubular stock. The cooling follows thesmoothing of the peripheral surface of the jacket, and the smoothing iscarried out under the influence of elevated temperatures. The coolingtakes place in a series of graduated cooling stages.

The method and apparatus disclosed in the aforementioned copendingapplication is concerned with the jacketing of tubular stock which isadvanced in a straight or substantially straight path which iscompletely or substantially completely horizontal. However, there arecircumstances where it is necessary or desirable that the path traversedby the tubular stock being jacketed is vertical or near vertical. On theother hand, the path must not be excessively long in these circumstancesbecause this would require very high installations, making accessdifficult, requiring large amounts of space, and presenting otherproblems.

The invention disclosed in the aforementioned copending applicationcannot be used for this purpose. It is, however, desirable to provide anapparatus which is capable of affording the jacketing of tubular stockin the manner disclosed in the aforementioned copending application, butwith the stock traveling in upright or near upright path.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to provide an apparatus affording the aforementionedadvantages.

More particularly it is an object of the present invention to provide anapparatus for jacketing-"preferably continuously--a relativelysmall-diameter tubular metallic stock advancing in a vertical or nearvertical path, with synthetic foam material.

A further object of the invention is to provide such an apparatus whichpermits the jacketing of such stock which is supplied and taken up inform of coils rotating about their respective axes, with the upper andlower coil being spaced by only a relatively small vertical distancefrom one another and with the material of this relatively small diametertubular stock being subjected to as little as possible of stretching anddeformation.

In pursuance of these objects, and others which will become apparenthereafter, one feature of the invention resides in an apparatus forcontinuous jacketing of metallic tubular stock with cellular syntheticplastic. This apparatus comprises, briefly stated, advancing means foradvancing tubular stock in downward direction and in a predeterminedpath which comprises at least some superimposed helical convolutions oflow pitch. Feed means and takeup means are provided for the tubularstock and are respectively arranged upstream and downstream of theadvancing means. Extruding means is arranged adjacent a first one of theconvolutions for extruding onto the outer circumferential surface of theadvancing tubular stock a circumferentially complete jacket of cellularsynthetic plastic. Forming means is adjacent a second convolutiondownstream of the first convolution for forming the peripheral surfacelayer of the thus-obtained jacket into a continuous smooth skin.Finally, cooling means is adjacent a third convolution downstream of thesecond convolution and serves for cooling the resulting jacketed tubularproduct.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic sideelevational view of an apparatus according to the present invention;

FIG. 2 is a horizontal longitudinal section through an extrusion headfor use in the apparatus of FIG. ll;

FIG. 3 is a view similar to FIG. 2 but illustrating a further extrusionhead;

FIG. 4 is a longitudinal section through a forming and smoothing devicefor use in the apparatus of FIG. ll;

FIG. 5 is a transverse section of the device shown in FIG. 4i;

FIG. 6 is a longitudinal section through a floating support for thejacketed tubular product, for use in the apparatus of FIG. 1;

FIG. 7 is a transverse section of the support shown in FIG. 6; and

FIG. 8 illustrates how opposite end portions of successive lengths of ajacketed tubular product can be connected with one another.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing indetail, and firstly FIG. ll, it will be seen that we have illustrated anapparatus for the continuous jacketed of metallic tubular stock ofrelatively small diameter. This apparatus comprises an upper payoffdevice utilizing a payoff drum 2 and a lower device for takeup utilizinga takeup drum 20. Both of the drums rotate in horizontal planes aboutupright axis of rotation and in the illustrated em bodiment the axes ofboth drums 2 and 2a are in alignment.

In the illustrated embodiment the vertical distance between the drums 2and 2a is only so large that the tubular stock lwhich is of metal and ofrelatively small diameter-passes downwardly from the upper coil 30carried by the drum 2 and reaches the lower drum 2a after traversingonly a few helical convolutions of relatively low pitch. It is taken uponto the drum 2a in form of a lower coil 30. According to the presentinvention it is advantageous that the diameter of the helicalconvolutions is at least substantially identical with the diameter ofthe coils 30 and 30a.

Intermediate the drums 2 and 2a and spaced from one another by adistance corresponding to somewhat more than two of the helicalconvolutions, are the advancing devices 3 and 3a. These define in thevertical space between themselves the path wherein the tubular stock isto be jacketed with a jacket of foamed synthetic plastic material.

The application of this jacket is accomplished by means of the extrusiondie 4i of an extruder 5. It is possible to provide the extrusion diewith an annular smoothing or forming means analogous or corresponding tothat disclosed in the aforementioned copending application.

However, in accordance with the present invention, the die may not beprovided with this device and a separate device 31 for forming andsmoothing of the peripheral surface of the applied jacket may beprovided. This device 31 will be described subsequently in more detail.

Downstream of the device 31 there is provided cooling means 11, 12 whichis diagrammatically illustrated and in the embodiment shown defines twosections which are supplied with cooling media of diflerent temperature.The first section is supplied with a cooling medium whose temperature ishigher than that of the second section so that the jacketed tubularproduct is cooled in two successive stages. Once the jacket is cooled inthis manner, it has its final strength so that the jacketed tubularproduct can then be advanced on roller supports 32 until it has passedthe lower advancing device 3a and reaches the lower drum 2a of thetakeup. It is advantageous that the advancing devices 3 and 3a besynchronously driven.

According to the invention it is advantageous that in the region of thecooling means 11, 12 the helical convolutions be supported by a floatingsupport 33. Several of these supports 33 may be provided and distributedin suitable manner. The smoothing or forming device 31 itself may alsofulfill the function of such a floating support or be replaced by one,that is if the extrusion die is provided with the annular type ofsmoothing or forming device disclosed in the copending application.

There is further provided an intermittently controlled cutting device,here illustrated as a saw 34, which advances in the direction and withthe speed of the jacketed tubular product, being arranged downstream ofthe advancing device 3a. A signal generating device 35 and a feeler orscanning device 36 are provided which cooperate with the saw 34 andwhich are located upstream of the advancing device 3a. The reason forthis arrangement is that is is customarywhen the jacket is to besupplied continuously to the advancing tubular stock, the ends ofsuccessive coils or lengths of tubular stock 1 are connected in themanner shown in FIG. 1 by means of an internal connector la. The devices35 and 36 detect the presence of such a connector la as it passes bythem and, in dependence upon the speed of advancement of the tubularstock 1, these devices activate the saw 34 which then saws through theconnector la intermediate the successive lengths of tubular stock 1 sothat the takeup drum 20 will always accept coils of a predeterminedlength.

The extrusion head 4 of the extruder 5 utilized in the apparatus of FIG.1 may be of the construction illustrated in FIGS. 2 or 3. A hollowmandrel 19 is provided in this case whose internal chamber 18 has adiameter greater than double the diameter of the tubular stock 1 whichis to be jacketed. The hollow mandrel 19 is illustrated as beingcomposed of two sections, namely the section 190, a tapered nipple ofwhich extends into the opening 37, and a rear section 19b which isprovided with threads cooperating with complementary threads in theadjusting sleeve 38 so as to be axially adjustable therein. An annularmember 39 is removably mounted intermediate the sections 19a and 19bapproximately at the middle of the hollow mandrel l9, and is providedwith a gliding guide 40 of sleevelike type which is offset in the mannerillustrated. A similar glide guide 41 is provided in a sleeve 20arranged at the inward side of the mandrel 19. These two guides 40 and41 which are offset lengthwise determine the precise position andmovement of direction of the metallic tubular stock 1 to be jacketed, sothat the same is surrounded-on passing the outlet 37 with which thenipple of the section 19a defines an annular concentric gap-is jacketedwith a jacket of preplasticized foamed synthetic plastic of a constantthickness. A guide sleeve 21 supports the mandrel l9 and is conicallytapered at its circumference. This guide sleeve 21 delimits an annularchamber 23 surrounding the mandrel 19 and being in turn surrounded bythe housing 24 and a member 24a. Synthetic plastic material is suppliedto the chamber 23 from the extruder via the conduit 22. The conduit 15communicating with the mandrel 19 is connected with a vacuum pump andthe annular member 39 may be provided with apertures so that the vacuumextends into the region of the extruder outlet.

In the embodiment illustrated in FIG. 2 the guide 40 is arrangedeccentrically and the tubular stock to be jacketed passes through theoutlet 37 with a slight curvature. By contrast, the embodiment of FIG. 3provides for the tubular stock to be jacketed to pass precisely coaxialthrough the outlet opening, and an inclined guide opening 40 andlongitudinal channels 42 are provided in the member 39. The end of themandrel 19 has a larger diameter and the sleeve 20 provided with theguide 41 is eccentric. In all other respects the construction of theextrusion head in FIG. 3 corresponds to that of FIG. 2.

Coming now to the forming or smoothing device illustrated in FIGS. 4 and5 it will be seen that it is provided with lower and upper members 43and 44 which will hereafter be identified as lamellas. They are offsetin comblike manner and it is preferable that the group of lamellas 44are transversely adjustable. The lamellas are provided with roundedglide edges. A housing surrounds the lamellas 43 and 44 and a liquid issupplied to the housing, with the liquid being tempered and serving tosupport the tubular stock in the manner of a liquid float support. Ofcourse, the liquid also acts as a glide means between the outercircumferential surface of the jacket and the pressure surfaces of thelamellas 43 and 44. A nozzle 45 may be provided at the inlet side of thedevice 31 for spraying liquid onto the first group of lamellas.

A specific glide or liquid support device 33 is illustrated in FIGS. 6and 7. It will be seen that jets of liquidsuch as water-are ejected withrequisite high pressure towards one another so that the jacketed tubularstock 1 is maintained in floating condition between these opposed jetsof liquid. Here, again, a nozzle ring 46 may be provided at the inletside of the device 33.

In the embodiment of FIG. 1 the tubular stock to be jacketed andadvancing downwardly from the upper coil 30 may move through helicalconvolutions having a radius of 1,000 mm. and a pitch of approximately800 mm. per convolution thus corresponding to a ratio of approximatelyl:8-towards the extrusion head. Approximately 800 mm. downstream of theextrusion head the now jacketed tubular stock whose jacket is alreadycooled to a large extent passes through one of the liquid supports andmoves out of the cooling device approximately after traversing anadditional helical convolution. Subsequently it is advantageous that thetubular product thus produced be dried.

It will be appreciated that with the apparatus according to the presentinvention the tubular stock to be jacketed which remains cold or coolover at least most of its path, is initially self-supporting withinlimits of its inherent elasticity, thereby eliminating materialdistortions. Because of the arrangement of the various components of thedevice intermediate and with reference to the supply and takeup drums 2,2a the installation cannot only be readily mounted, but also requiresrelatively little space and is easily accessible and easily observable.The various components of the apparatus which act upon the tubularstocksuch as the extrusion head, the cooling means and the likesupportthe convolutions of the tubular stock and thus prevent undesireddeformations thereof. Because of the vertical spacing of the drums 2 and2a the portion of the path in which jacketing occurs is under constantprecise control so that the jacket of synthetic plastic material issuingfrom the extruder headwhich jacket is already self-supporting but notyet finally cured or hardenedis subjected to none or only insignificantsurface tensions and forces as it passes through the forming device andthe cooling device. Thus, although the tubular stock 1 is of smallerdiameter and thin walled, undesired deformations and other stresses uponthe material are excluded completely or almost completely while yet thedesirable configuration of the tubular stockprior to and subsequent tojacketing-in form of coils is maintained.

The floating support devices need or need not be provided, but they arehighly advantageous because they do not affect the surface consistencyof the jacket and the frictional resistance to movement is insignificantbecause the tendency to continue the helical downward movement ismaintained only under the weight of the respective increment of jacketedtubular stock. It is advantageous that such a floating liquid support belocated substantially at the midpoint of the cooling stages. However,the floating liquid support may be replaced inter mediate the extrusionhead and the cooling stages with the device illustrated in FIGS. 4 and 5in which case the liquid not only serves to provide floating support butalso acts as a glide means.

By utilizing one of the extrusion heads illustrated in FIGS. 2 and 3 itis possible to have the tubular stock issue from the outlet of theextrusion head coaxially therewith or add a small inclination. Theextrusion head itself need not be changed but at the same time adequatespace is provided by use of this particularly configurated hollowmandrel 19 for guidance of the curved increments of tubular stock. Thesleevelike guides can be readily replaced if necessary and it isadvantageous according to the invention if bores through which thetubular stock passes in the guides and in the outlet of the extrudinghead extend tangentially to the curved increment of tubular stock. Bymaking the hollow mandrel 19 of two sections it is possible to readilyreplace either section when necessary, and the relatively large spacebetween the sections serves at the same time for connection to a vacuumconduit.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofapplications differing from the types described above.

While the invention has been illustrated and described as embodied in anapparatus for continuous jacketing of metallic tubular stock of cellularsynthetic plastic, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. Apparatus for continuous jacketing of metallic tubular stock withcellular synthetic plastic, comprising advancing means for advancingtubular stock in downward direction and in a predetermined path whichcomprises at least some superimposed helical convolutions of low pitch;feed means for said tubular stock arranged upstream and upwardly of saidad vancing means for feeding said tubular stock thereto; extruding meansadjacent a first one of said convolutions downwardly of said feed meansfor receiving the advancing tubular stock therefrom and for extrudingonto the outer circumferential surface of the advancing tubular stock acircum ferentially complete jacket of cellular synthetic plastic;forming means adjacent a second convolution downstream of said firstconvolution and arranged to receive the jacketed stocks from saidextruding means for forming the peripheral surface layer of the jacketinto a continuous smooth skin; cooling means downwardly spaced alongsaid path from said forming means and located adjacent a thirdconvolution downstream of said second convolution for cooling theresulting jacketed tubular product; and takeup means for said jacketedtubular product downwardly spaced from said cooling means for receivingand taking up the cooled jacketed tubular product.

2. Apparatus as defined in claim ll, wherein said feed means and saidtakeup means comprise drums rotatable about resgpective upright axes ofrotation.

. Apparatus as defined in claim 2, wherein said axes are at leastsubstantially coaxial.

4. Apparatus as defined in claim 2, each of said drums supporting a coilof tubular stock of predetermined outer diameter and wherein thediameter of said convolutions is at least substantially equal to saidpredetermined outer diameter of at least one of said coils.

5. Apparatus as defined in claim 2, wherein said advancing meanscomprises an upper and a lower advancing device; and wherein saidadvancing devices are synchronously driven.

6. Apparatus as defined in claim 2, said extruding means comprising anextruding die through which said tubular stock advances and wherein itreceives said jacket; and further comprising liquid-support meansdownstream of said extruding die at least in the region of said coolingmeans for supporting the jacketed tubular product advancing in saidpath.

7. Apparatus as defined in claim 6, said forming means being liquidoperated and comprising a plurality of forming members having respectivefree edges which define with one another a passage through which thejacketed tubular stock is compelled to pass in contact with said freeedges.

8. Apparatus as defined in claim 7, wherein said forming members areadjustable with reference to one another.

9. Apparatus as defined in claim 2, said extruding means comprising anextruding die defining a passage, a hollow mandrel in said passage anddefining therewith an annular extrusion gap coaxial with said passage,said mandrel having an inlet portion, an outlet portion and anintermediate portion; wherein said hollow mandrel has an inner diametermore than twice the outer diameter of said tubular stock; and furthercomprising replaceable guide means in the region of said inlet andintermediate portions for guiding the tubular stock advancing in ahelical convolution through said mandrel.

10. Apparatus as defined in claim 9, :said guide means and said outletportion having openings for said tubular stock which extend tangentiallyto the curvature of said tubular stock.

1111. Apparatus as defined in claim 9, said mandrel comprising twoaxially adjacent sections, and wherein said guide means comprises anannular guide member located between said sections.

12. Apparatus as defined in claim 5; further comprising cutter meanslower of said downstream advancing device and arranged for movement insaid path and at the speed of said jacketed tubular product.

i3. Apparatus as defined in claim l2; and control means forintermittently controlling said cutter means.

14. Apparatus as defined in claim 13, said control means comprisingfeeler means and signal-generating means operated by said feeler meansand operative for controlling said cutter means, said feeler means andimpulse-generating means being arranged upstream of said lower advancingdevice.

1. Apparatus for continuous jacketing of metallic tubular stock withcellular synthetic plastic, comprising advancing means for advancingtubular stock in downward direction and in a predetermined path whichcomprises at least some superimposed helical convolutions of low pitch;feed means for said tubular stock arranged upstream and upwardly of saidadvancing means for feeding said tubular stock thereto; extruding meansadjacent a first one of said convolutions downwardly of said feed meansfor receiving the advancing tubular stock therefrom and for extrudingonto the outer circumferential surface of the advancing tubular stock acircumferentially complete jacket of cellular synthetic plastic; formingmeans adjacent a second convolution downstream of said first convolutionand arranged to receive the jacketed stocks from said extruding meansfor forming the peripheral surface layer of the jacket into a continuoussmooth skin; cooling means downwardly spaced along said path from saidforming means and located adjacent a third convolution downstream ofsaid second convolution for cooling the resulting jacketed tubularproduct; and takeup means for said jacketed tubular product downwardlyspaced from said cooling means for receiving and taking up the cooledjacketed tubular product.
 2. Apparatus as defined in claim 1, whereinsaid feed means and said takeup means comprise drums rotatable aboutrespective upright axes of rotation.
 3. Apparatus as defined in claim 2,wherein said axes are at least substantially coaxial.
 4. Apparatus asdefined in claim 2, each of said drums supporting a coil of tubularstock of predetermined outer diameter and wherein the diameter of saidconvolutions is at least substantially equal to said predetermined outerdiameter of at least one of said coils.
 5. Apparatus as defined in claim2, wherein said advancing means comprises an upper and a lower advancingdevice; and wherein said advancing devices are synchronously driven. 6.Apparatus as defined in claim 2, said extruding means comprising anextruding die through which said tubular stock advances and wherein itreceives said jacket; and further comprising liquid-support meansdownstream of said extruding die at least in the region of said coolingmeans for supporting the jacketed tubular product advancing in saidpath.
 7. Apparatus as defined in claim 6, said forming means beingliquid operated and comprising a plurality of forming members havingrespective free edges which define with one another a passage throughwhich the jacketed tubular stock is compelled to pass in contact withsaid free edges.
 8. Apparatus as defined in claim 7, wherein saidforming members are adjustable with reference to one another. 9.Apparatus as defined in claim 2, said extruding means comprising anextruding die defining a passage, a hollow mandrel in said passage anddefining therewith an annular extrusion gap coaxial with said passage,said mandrel having an inlet pOrtion, an outlet portion and anintermediate portion; wherein said hollow mandrel has an inner diametermore than twice the outer diameter of said tubular stock; and furthercomprising replaceable guide means in the region of said inlet andintermediate portions for guiding the tubular stock advancing in ahelical convolution through said mandrel.
 10. Apparatus as defined inclaim 9, said guide means and said outlet portion having openings forsaid tubular stock which extend tangentially to the curvature of saidtubular stock.
 11. Apparatus as defined in claim 9, said mandrelcomprising two axially adjacent sections, and wherein said guide meanscomprises an annular guide member located between said sections. 12.Apparatus as defined in claim 5; further comprising cutter means lowerof said downstream advancing device and arranged for movement in saidpath and at the speed of said jacketed tubular product.
 13. Apparatus asdefined in claim 12; and control means for intermittently controllingsaid cutter means.
 14. Apparatus as defined in claim 13, said controlmeans comprising feeler means and signal-generating means operated bysaid feeler means and operative for controlling said cutter means, saidfeeler means and impulse-generating means being arranged upstream ofsaid lower advancing device.